Method of manufacturing high strength fiber reinforced thermo plastic parts

ABSTRACT

The method includes a shaping step utilizing the good shaping characteristics of thermoplastic material prior to the application of local fiber reinforcement. After shaping high strength fiber reinforcement is applied in the form of tapes. Both adhesive and base material matrix bonding methods of securing the reinforcing tapes are contemplated. For finished parts, that require a smooth surface, it is possible to mold a recess into the surface of the thermoplastic material to accommodate the tape and produce a substantially continuous smooth outer surface.

'United States Patent [191 Long [ METHOD OF MANUFACTURING HIGH STRENGTHFIBER REINFORCED THERMO PLASTIC PARTS [75] Inventor: Roger A. Long,Escondido, Calif.

[73] Assignee: Teledyne Ryan Aeronautical a Division of TeledyneIndustries, Inc., San Diego, Calif.

22 Filed: Oct. 25, 1972 21 Appl. No.: 300,846

[52] U.S. Cl. 156/242; 156/293; 156/306; 264/92; 264/257 [51] Int. ClB29b 23/00 [58] Field of Search 156/242, 245, 500, 166, 156/176, 178,293, 306; 264/90, 92, 257, 258

[56] References Cited UNITED STATES PATENTS Wai Hui et al. 156/178Zimmerman 264/92 Kramer 156/245 Dec. 16, 1975 Heider et a1. 156/5003,349,157 10/1967 Parsons 264/258 3,516,122 6/1970 Schwartz 264/923,682,749 8/1972 Schrenk 156/500 3,755,035 8/1973 Olson et al 156/245Primary Examiner-Daniel J. Fritsch Attorney, Agent, or FirmBrown &Martin [5 7] ABSTRACT The method includes a shaping step utilizing thegood shaping characteristics of thermoplastic material prior to theapplication of local fiber reinforcement. After shaping high strengthfiber reinforcement is applied in the form of tapes. Both adhesive andbase material matrix bonding methods of securing the reinforcing tapesare contemplated. For finished parts, that require a smooth surface, itis possible to mold a recess into the surface of the thermoplasticmaterial to accommodate the tape and produce a substantially continuoussmooth outer surface.

6 Claims, 3 Drawing Figures US. Patent Dec. 16, 1975 METHOD OFMANUFACTURING HIGH STRENGTH FIBER REINFORCED THERMO PLASTIC PARTSBACKGROUND OF THE INVENTION The range of applications for thermoplasticand plastic composite materials have been increasing rapidly in recentyears. However the extent to which thermoplastics can be utilized inhigh load environments has been severely limited. One of the limitationsresults when reinforcing in the form of fiber reinforcement isincorporated, the plastic looses its formability. Because formability isone of the chief characteristics in plastic that make it economicallycompetitive with more conventional structural materials, the reductionin this formability by the incorporation of fiber reinforcement isnormally sufficiently costly to make such high strength applicationsimpractical. High strength applications are particularly difficult wherethe final part configuration must have complex curvatures requiringrelatively severe formability requirements.

In those prior art techniques that incorporate fibers in the plasticmaterial to be formed, it has normally been a requirement thatrelatively expensive and high initial cost tooling be utilized.Therefore such prior art techniques are suitable only where high unitcosts are acceptable or in extremely large production quantities.

Therefore it is desirable to have a method of manufacturing highstrength fiber reinforced plastic parts that permit the formation ofplastic parts while the plastic base material is in an easily shapedcondition, and thereafter reinforcing selectively the plastic formedconfiguration to produce a high strength composite structure. Such aprocess is particularly desirable in that it is adaptable to relativelylow production runs and maintains a low unit cost with low initial costtooling.

SUMMARY OF THE INVENTION According to an exemplary embodiment of theinvention, theremoplastic material such as polycarbonates, ABS,acrylates, nylons, and polypropylenes with their good formabilitycharacteristics, are mated with long length collimated, paralleloriented fiber, in a method that joins the high strength long lengthfibers to the base material after shaping is completed. Fibers may be ofglass, organics, graphite, boron, or other suitable high strengthfibers.

The aforementioned sheet theremoplastics typically soften sufficientlyto make them easily formable at temperatures in the range of 200 to400F. Thus in the normal practice of the invention, where plastic insheet form is employed, the materials would be heated to the temperatureat which softening takes place, and then secured over a vacuum formingmale mold. The vacuum source would then be applied to draw the sheetmaterial onto the mold form. After forming, the configured plastic sheetwould be removed from the vacuum forming machine and the fibers in theform of prealigned fiber-matrix tape applied at selected high stresslocations. For example, in the forming of components utilized in themanufacture of aircraft, the parts may be formed with a recess toreceive reinforced fiber tape along the longitudinal centerline of theaircraft to reinforce against major longitudinal bending stresses.Similarly, reinforced tapes could be applied along the wing skins toincrease the stiffness of the wing structure.

It is within the concept of the invention to secure the tape to the basematerial by utilizing a tape comprised of fibers in a matrix of eitherthe base thermoplastic material or a compatible plastic. In thispractice of the invention, the part adjacent to the tape area would beheated to a temperature at which the base material in the tape and partwould join to form a welded permanent bond. However, adhesive bonding ofthe tape to the part through the use of an anaerobic adhesive hasparticular advantages in the process of the invention. Such an anaerobicadhesive, because it does not require a cure temperature to set, is mosteasily applied and will transfer the necessary shear forces to enablethe skin reinforcement effect of the fiber reinforced tape to be fullyutilized. Adhesive bonding by the use of heat curing adhesives is alsocontemplated where curing at some elevated temperature is notdetrimental.

Whereas vacuum forming has particular advantages where relatively lowcost tooling is desirable, it may also be desirable to utilize aninjection molding process wherein the plastic material is provided inbead form, and is melted and injected into a mold so as to expand intoeither a plastic foamed type material or a solid material. Such foammaterial when shaped into a mold cavity at an appropriate temperature,forms a foamed center section with solid plastic skin portions, and itis to this skin portion that the reinforcing is applied.

It is therefore an object of this invention to provide a new andimproved method of manufacturing high strength fiber reinforcedthermoplastic parts.

It is another object of the invention to provide a new and improvedmethod of manufacturing thermoplastic parts that results in a highstrength, low cost finished part.

It is another object of this invention to provide a new and improvedmethod of forming thermoplastic parts that permits the plastic part tobe formed when it is at its optimum formable condition.

It is another object of this invention to provide a new and improvedthermoplastic part that takes optimum advantage of fiber reinforcing.

It is another object of this invention to provide a new and improvedmethod of manufacturing thermoplastic parts that enables long lengthfibers to be utilized.

It is another object of this invention to provide a new and improvedmethod of manufacturing thermoplastic parts that is susceptible to highvolume production.

It is another object of this invention to provide a new and improvedmethod of manufacturing thermoplastic parts wherein skin reinforcing ofthe plastic material is provided.

Other objects and many advantages of the method of the invention willbecome more apparent from a reading of the following detaileddescription, together with the drawings, wherein like reference numeralsdesignate like parts throughout and in which:

FIG. 1 is a perspective view of a typical molded part separated from itsmold.

FIG. 2 is a view of the part inverted to illustrate the addition ofstiffening and reinforcing tapes.

FIG. 3 is a perspective view of an alternative mold and the part formedwith tapes received in prepared recesses.

Referring to the drawings, there is illustrated a part 10 in the form ofa section of an aircraft configuration formed over a mold 11 andincluding a nose and fuselage portion 12 and two generally delta shapewing sections 14 and 16. The method of the invention has particularapplicability to the forming of large aircraft parts such as the overallbody configuration illustrated. Such parts may be most convenientlyformed utilizing vacuum forming techniques and from large sheets of thethermo setting plastic material. However, the plastic material, unaidedby reinforcing, is not capable of withstanding the stresses anticipatedin normal flight regimes without being of excessive thicknesses andtherefore having no low weight and cost benefits. Therefore after thepart has been vacuum formed and cooled to harden the configuration,fiber tapes, such as tapes l8 and 20 illustrated in FIG. 2, are appliedat the critical stress locations. For the configuration illustrated thetapes are applied to the underside or interior face and along theleading edges of the wing shape. Since these tapes are on the interiorof the fuselage form, and therefore need not be faired into the surfaceof the material for aerodynamic purposes, it is possible to apply thetapes directly to the smooth formed plastic material. Alternatively, asin the situation illustrated in FIG. 3, where the tapes are to beapplied to the exterior skin of the material, a recess such as recess 22may be formed. The mold 26 is formed with a channel 28 so that, as theplastic sheet 30 is pulled down over the mold, the recess 22 will formin the outer surface of the part. After removal from the mold and cooleddown, it is possible to apply the external stiffening tape 32 into therecess 22 and thereby produce a faired surface with desirableaerodynamic characteristics.

The tapes utilized in the exemplary embodiment of the inventionincorporate a high volume percentage (in excess of 50%) of collimatedparallel fibers in excess of 1 inch length. Several layers of the tapemay be laid up one upon the other, with each layer having a thickness upto mils.

In some instances it may be desirable to mold the part with thestiffener already in place. This capability is also illustrated in FIG.3 wherein a stiffener 34 is placed on the interior of the sheet materialprior to forming and is formed over the male mold and into the groove 36during the vacuum forming process.

The step of applying the elongated fiber tape to the plastic surface maybe accomplished through the use of a tape including a matrix materialidentical to or structurally and physically compatible with the basematerial. As a variation to this basic approach, it may be desirable toincorporate a matrix material having characteristics that are midwaybetween those of the fiber and the base material. An example of thisapplication would be where it is desirable to use fibers having asignificantly lower thermal coefficient of expansion than that of theplastic base material. In this instance, a matrix material for the fibertape would be selected to have a thermal coefficient of expansionapproximately midway between that of the base material and that of thefibers. With either of the foregoing approaches, it is possible to heatthe part to that temperature at which the matrix and base materialsoften sufficiently to promote a welded permanent and integral bonding.

A second and important bonding approach utilized with the invention isthat of adhesive bonding. Various adhesives including epoxy basedadhesives and adhesive techniques may be utilized at room temperature orat elevated temperatures to produce a bond having sufficient strength inshear between the fiber reinforced tape and the plastic based materialso that sufficient load is transferred to the fibers to take advantageof their high strength high modulus characteristics.

Of the various adhesives available, the use of anaerobic adhesives isparticularly indicated in the practice of the invention. Anaerobicadhesives develop bonding adhesion when pressure between the tape andpart is applied and no elevated temperature curing cycles are requiredand they are particularly adaptable to high volume operation.

Plastic parts shaped and reinforced according to the teachings of theinvention are not significantly heavier than those not incorporatingreinforcing. While the parts illustrated in the figures show highlyselective reinforcement at only those high stress locations where it isa prime prerequisite, the method of the invention suggests itself to usewhere fiber volume contents between 5 and 50 percent are utilized. Theserelatively high fiber contents can be obtained, despite the fact thatthe finished part has a high percentage of compound curves and otherdifficult to form configurations, which configurations would beimpossible to form with plastic composites made from fiber containingsheet material. This is particularly true where long fibers areinvolved. Long fibers are to be preferred where possible over shorterfibers in that the high strength or high modulus characteristics arebest taken advantage of with fibers of this length. However, long lengthstiff fibers in sheet material make the materials difficult is notimpossible to form and thus the invention enables the production ofparts which take advantage of having long length, high strength, highmodulus fibers and yet have the design contours required.

In a specific application of the invention 6.1 volume percent graphitefibers were used to locally reinforce AZDEL A-200 plastic. AZDEL A-200plastic is a glass fiber reinforced thermo plastic sheet based onstyreneacrylonitrle copolymer and is made by g.r.t.l. Company ofSouthfield, Mich. Room temperature tensile strength increased 20%, andthe tensile modulus increased 180%. At F test temperature, the tensilestrength increased 38% and the tensile modulusincreased 200%.

Having described my invention, I now claim.

1. A method of forming high-strength fiber-reinforced thermo plasticparts comprising the steps of,

heating thermo plastic material to a temperature at which it is readilyformable,

forming said material to the desired final configuration by drawing saidmaterial by a vacuum onto a mold,

permitting said plastic material to cool and harden,

applying an elongated fiber reinforcing to selective locations on atleast one of said surfaces of said material by placing tapes ofelongated high strength, and high modulus fibers in a matrix of thermoplastic material onto the surface of the formed thermo plastic part,

bonding said tapes at said selective locations by heating said thermoplastic matrix material in said tapes.

2. The method of claim 1 wherein said step of forming is furthercharacterized by relieving the surface of the plastic material toprovide recesses for receiving tapes of elongated fibermatrix material.

3. A method of forming high strength fiber reinforced thermo plasticparts comprising the steps of,

heating thermo plastic material to a temperature at which it is readilyformable,

forming said material to the desired final configuration by drawing saidmaterial by a vacuum onto a mold,

permitting said plastic material to cool and harden,

adhesively bonding tapes of elongated high strength and high modulusfibers in a matrix material onto the surface of the formed thennoplastic part at selected locations.

4. The method as claimed in claim 3 wherein,

said step of forming is further characterized by relieving the surfaceof the plastic material to provide recesses for receiving tapes ofelongated fiber matrix material.

5. A method of forming high strength fiber reinforced thermo plasticparts comprising the steps of,

heating thermo plastic material to a temperature at which it is readilyformable,

forming said material to the desired final configuration,

permitting said plastic material to cool and harden,

placing tapes of elongated high strength and high modulus fibers in amatrix of thermo plastic material onto the surface of said thermoplastic material,

bonding said tapes in position on the formed thermo plastic part byheating the matrix material to a temperature at which it bonds to saidformed thermo plastic part.

6. The method as claimed in claim 5 wherein,

said step of forming is further characterized by reliev ing the surfaceof said plastic material to provide recesses for receiving tapes ofelongated fiber matrix material.

1. A METHOD OF FORMING HIGH-STRENGTH FIBER-REINFORCED THERMO PLASTICPARTS COMPRISING THE STEPS OF, HEATING THERMO PLASTIC MATERIAL TO ATEMPERATURE AT WHICH IT IS READILY FORMABLE, FORMING SAID MATERIAL TOTHE DESIRED FINAL CONFIGURATION BY DRAWING SAID MATERIAL BY A VACUUMONTO A MOLD, PERMITTING SAID PLASTIC MATERIAL TO COOL AND HARDEN,APPLYING AN ELONGATED FIBER REINFORCING TO SELECTIVE LOCATIONS ON ATLEAST ONE OF SAID SURFACES OF SAID MATERIAL BY PLACING TAPES OFELONGATED HIGH STRENGTH, AND HIGH MODULUS FIBERS IN A MATRIX OF THERMOPLASTIC MATERIAL ONTO THE SURFACE OF THE FORMED THERMO PLASTIC PART,BONDING SAID TAPES AT SAID SELECTIVE LOCATIONS BY HEATING SAID THERMOPLASTIC MATRIX MATERIAL IN SAID TAPES.
 2. The method of claim 1 whereinsaid step of forming is further characterized by relieving the surfaceof the plastic material to provide recesses for receiving tapes ofelongated fiber-matrix material.
 3. A method of forming high strengthfiber reinforced thermo plastic parts comprising the steps of, heatingthermo plastic material to a temperature at which it is readilyformable, forming said material to the desired final configuration bydrawing said material by a vacuum onto a mold, permitting said plasticmaterial to cool and harden, adhesively bonding tapes of elongated highstrength and high modulus fibers in a matrix material onto the surfaceof the formed thermo plastic part at selected locations.
 4. The methodas claimed in claim 3 wherein, said step of forming is furthercharacterized by relieving the surface of the plastic material toprovide recesses for receiving tapes of elongated fiber matrix material.5. A method of forming high strength fiber reinforced thermo plasticparts comprising the steps of, heating thermo plastic material to atemperature at which it is readily formable, forming said material tothe desired final configuration, permitting said plastic material tocool and harDen, placing tapes of elongated high strength and highmodulus fibers in a matrix of thermo plastic material onto the surfaceof said thermo plastic material, bonding said tapes in position on theformed thermo plastic part by heating the matrix material to atemperature at which it bonds to said formed thermo plastic part.
 6. Themethod as claimed in claim 5 wherein, said step of forming is furthercharacterized by relieving the surface of said plastic material toprovide recesses for receiving tapes of elongated fiber matrix material.